When we eat table sugar (sucrose), it is made up of 50% glucose and 50% fructose. When these simple sugars arrive at the liver for processing, one of three things happen. First, they can be released into the blood to be used for energy. Next, they can be either stored in the liver or sent to the muscles and stored as glycogen (a secondary source of energy which we will come to later). Thirdly, the liver will convert excess glucose and all fructose (yes, all fructose) into saturated fat. The vast majority of the fat, if not all of the fat that ends up in the arteries and in LDL, is synthesised in the liver from sugars (fructose and glucose) in a process known as ‘de novo lipogenesis’. All of the fat synthesised is saturated fat and most of it palmitic acid. What makes this interesting is that the type of saturated fat synthesised is palmitic acid, which is the fat most likely to cause cardiovascular disease (CVD). This is really critical to understand, because many dietitians tell people to cut down on any food that includes palmitate acid. However, the palmitic acid in the arteries that can cause CVD, biologically has to have originated from CARBS.
What is interesting is that of the two simple sugars, the one that is usually turned into saturated fat is fructose. In fact, it seems that no fructose is released from the liver into the bloodstream. Think about this logically; we have blood glucose measurements and a glycaemic index, but never fructose measurements. It’s also why people with diabetes only ever measure glucose in the blood.
This fat fact is vital to understand if you are to recognise that all of those headlines you hear about the dangers of eating saturated fat are wrong. The dangerous saturated fat is the one that, through lipogenesis, we synthesise ourselves, as a way to deal with deadly sugar. It is important to understand that it is almost impossible for fat that we eat to create very low-density lipoproteins (VLDL), which then becomes LDL. It is the synthesis of CARBS, in particular fructose, that is the sole contributor and building block of LDL. This is basic human physiology.
An investigation recently found that in 1960 the American Sugar Industry paid Harvard researchers to produce a clinical paper stating that it was the intake of fat, not sugar, that causes CVD. Once you understand basic human physiology and novo lipogenesis, you realise this is entirely untrue. In fact, it is believed that over time, it is fructose that is a contributing factor to both CVD and to non-alcoholic fatty liver disease (NAFLD). Where does fructose come from? Table sugar, soft drinks, fruit and high fructose corn syrup.